#btn {
    position: fixed;
    right: 10px;
    bottom: 10px;
    cursor: pointer;
    animation: move 2.5s cubic-bezier(0.45, 0.05, 0.55, 0.95) infinite;
}

@keyframes move {
    0% {
        bottom: 0%;
    }
    50% {
        bottom: 5%;
    }
    100% {
        bottom: 0%;
    }
}